powerpc/64s: Move __replay_interrupt function below handlers

This is not an exception handler as such, it's called from
local_irq_enable(), not exception entry.

Also clean up some now redundant comments at the end of the
consolidation series.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>